A number of beverage glass washers have heretofore been commercially available, and patent literature contains proposals for many more; but all such prior art machines suffer from one or more of a number of important deficiencies, notwithstanding that the art relating to such machines is relatively old and well developed and the public health implications of beverage glass sanitization are well understood and widely appreciated.
A basic requirement for a glass washer is absolute reliability. A busy restaurant or tavern cannot practicably have enough beverage glasses to operate through a full day without washing at least some of them. Mechanical failure of the glass washer therefore puts the establishment out of business until the machine is back in operation, because there is almost never a backup for the glass washing machine, especially in the many jurisdictions where manual washing of beverage glasses is prohibited.
A more serious problem arises when the machine continues to run but does not effect complete sanitization of the glasses passed through it. The term "sanitization" is used herein to denote both cleaning and sterilization. Thus an adequate sanitization process must include a wash with a detergent solution at a temperature of at least 120.degree. F., for removal of soil such as lipstick, followed by a rinse with a germicidal solution of chlorine, iodine or the like. Applicable laws and regulations require these solutions to have prescribed minimum concentrations of the respective chemicals.
Most prior glass washing machines have been designed for reliance upon a daily check of the detergent and germicide reservoirs to ensure that these requirements will be met. Because such a check may be neglected or carelessly performed, some machines have lamps or the like that signal the need for replenishing the chemical supplies, but observations of such machines under actual operating conditions have revealed that their signals are sometimes unnoticed or disregarded for hours or even days at a time, thus subjecting the public to serious health hazards. In the light of this unexpected finding, the present invention is in part based upon an appreciation of the heretofore unrecognized requirement that a glass washing machine should in some manner impose upon its operator an absolute requirement for maintaining an adequate supply of detergent and germicide in its chemical reservoirs, and that the most effective way to accomplish this is to cause the machine to stop when a chemical is not being fed at an adequate rate.
To this end, solution concentration can be monitored by means of a pair of electrodes immersed in the solution, for measuring its electrical conductivity or resistance. The reliability of such a detector is dependent upon the water and chemicals used in the washing process and also to some extent upon the types of beverages served in the glasses to be washed. Certain substances present in the water or chemicals can cause deposits on the electrodes that result in false outputs. Salt or fruit acids in the washing liquid, introduced from glasses that have been used for margaritas or the like, can materially change in the conductivity of the liquid and can likewise cause false indications. The present invention therefore provides a more reliable means for monitoring solution concentration and causing the machine to stop when a chemical supply needs to be replenished.
Provision of adequate hot water involves a complex of problems. Some prior glass washers had no provision for heating incoming water. They were intended to be connected with an external hot water source, but all too often the hot water capacity of that source was insufficient, and at times, therefore, such glass washers operated with water too cool to ensure complete sanitization. On the other hand, a water heater built into the machine must be capable of bringing a large volume of water quickly up to a required temperature and must nevertheless operate with the lowest possible current consumption. Water heating economy is dependent not only upon the efficiency of the heating equipment itself but also upon the manner in which the machine is operated as well as upon its recirculation scheme.
For high volume glass sanitization, a glass washing machine should be so arranged that dirty glasses can be loaded into it and clean glasses can be unloaded from it while it is operating. Most prior machines that meet this requirement had a linear conveyor with a loading end onto which dirty glasses were placed and an unloading end from which clean glasses were removed and were designed on the assumption that the machine would be turned off when not needed. That assumption has been found to be incorrect. In a test, such a glass washer, installed in a busy restaurant, was equipped with suitable metering devices and, under typical conditions, was found to have been left running continuously for eight hours, during which it was actually washing glasses through a total of only two hours. This meant that during 75 per cent of its eight hour running time, water, chemicals and current were being wasted at substantial cost. With this in mind, the present invention provides a control mechanism for a continuous-process glass washer whereby the machine is allowed to operate only when it can operate usefully.
An important consideration in this respect is that the machine should not ordinarily be allowed to operate when only a few glasses have been loaded into it. About as much water, chemicals and current are needed for cleansing one glass as for a full capacity load of glasses. Thus another problem solved by the invention is that of providing for so controlling the machine that it operates only when and as it is loaded for operation at maximum efficiency.
The prior art discloses several kinds of glass sanitization cycles wherein sanitizing liquids are recirculated in the machine for conservation of water, heat and chemicals. One might suppose that design of an optimum sanitizing cycle and recirculation scheme would involve little more than selection from among a relatively limited number of combinations and permutations; but in fact the prior art demonstrates that the problem does not have such an obvious solution because no completely satisfactory arrangement has heretofore been devised. U.S. Pat. No. 3,094,997, to Nolte et al, disclosed a washer having one wash stage in which wash water was recirculated and one rinse stage wherein the rinse water was (depending upon the operator's choice) drained and thus wasted or delivered into the tank from which wash water was recirculated, to thus dilute the wash water detergent concentration. U.S. Pat. No. 3,731,696, to Hackney, discloses a glass washer having washing, first rinse and final rinse stages, wherein the liquid used for each stage was recirculated for exclusive use within that stage. From a sanitary standpoint the arrangement was perhaps suitable for the small batch-type washer in which it was disclosed, but it would not have been satisfactory for a continuous-process washer. Somewhat superior in this respect was the substantially earlier U.S. Pat. No. 1,681,839, to Breton, disclosing a plural stage washer wherein liquid from each stage was recirculated back to a preceding stage to move progressively from the cleanest to the dirtiest glasses; but here the washing liquid would be subjected to constant dilution of its detergent content. Since the germicidal rinse liquid can be substantially cooler than the detergent solution, this arrangement was also wasteful of water heating energy. A more recent arrangement, disclosed in U.S. Pat. No. 3,878,856, to Hall, has some advantages over those discussed above in that the washer has a washing stage wherein washing liquid is recirculated, followed by first and final rinse stages, the rinsing liquid used in the final rinse stage being in part recirculated in that stage and in part delivered back to the first rinse stage, where it is discharged to drain immediately after use. Recirculation of the final rinse liquid cannot be considered altogether objectionable in view of the fact that final rinse follows a first rinse, but one can question the logic of recirculating final rinse liquid in the face of the fact that liquid that has been used for the less critical first rinse is not recirculated.
The prior art, which is merely exemplified by the above discussed patents, teaches that the sequence of sanitizing stages and the recirculation scheme are interrelated and have a direct bearing on economy of operation and attainment of complete sanitization, but it does not teach the arrangement that is optimum in these respects, particularly for a continuous-process machine. Furthermore, the present invention is in part based upon recognition that the recirculation scheme also has a relationship to dependable operation of the washer, to maintenance of a constant inflow of makeup water that prevents excessive contamination of recirculated liquid, and to accurate maintenance of required detergent and germicide concentrations in the respective washing and rinsing liquids.
A problem which is intimately related to the recirculation scheme, and which has a direct bearing upon reliability of operation as well as upon economy of operation, is that of nozzle plugging.
In most washers, glasses are cleaned by subjecting them to spray or jets from numerous nozzles, each of which has a relatively small discharge outlet that is easily blocked by a bit of foreign matter. Glasses loaded into the washer often contain particles of fruit pulp, small berry seeds, or even paper napkins or cigarette butts, and such materials must obviously be prevented from being carried into the nozzles by recirculated liquid.
Of course screens have been incorporated in the recirculation systems of prior washers, but such screens have not been arranged to provide total insurance against nozzle blockage. In most cases the screen had to be removed for cleaning and its removal often permitted bits of material that had accumulated in the recirculation system upstream from the screen to pass the screen location and enter the duct leading to a set of nozzles, giving rise to the blockage that the screen was intended to prevent.
The screens in most prior recirculation systems were so arranged that foreign matter continued to accumulate on them until they were cleaned. Such an accumulation could reach a point where the screen was substantially blocked. Either a blocked screen or a blocked nozzle will cause a reduction in the amount of recirculating liquid being discharged against glasses and can thus be responsible for incomplete sanitization. However, most prior machines had no means for signaling that a screen needed cleaning or that a nozzle was blocked, and often the known blockage of one or a few nozzles was ignored because of the cost or inconvenience of remedying the condition. With this in mind, the present invention proceeds from a recognition that a glass washing machine should be caused to stop operating whenever an insufficient flow of any cleansing liquid is being discharged against glasses to be cleaned.